1. Field of the Invention
The present invention relates to absorbent articles for body fluid, such as sanitary napkins, paper diapers, surgical pads and breast milk sheets. In particular, the present invention relates to an absorbent article comprising an absorbent element which partially or wholly comprises an absorbent sheet made from an absorbent material having liquid absorbent (or retentive) power and an absorbent polymer weakly fixed on the absorbent material with a pressure-sensitive adhesive applied thereto in the form of a dot, a line or a curve.
1. Description of the Prior Art
The absorbent element of conventional absorbent articles such as sanitary napkins or paper diapers mainly comprises a fluffy pulp, an absorbent paper and an absorbent polymer. Among them, a highly absorbent polymer is present in most of the absorbent articles at present, since it has a high absorption capacity and solidifies the fluid into a gel so that the fluid cannot leak out once absorbed.
In spite of having such excellent characteristics, however, the absorbent polymer has a technical problem in that it tends to fall off i.e., it easily leaks out of the absorbent article, since it is powdery. In addition, there is a demand to further improve the essential absorption capacity of the absorbent polymer. Since the falling off of the absorbent polymer is a fatal defect for the absorbency properties of the absorbent article, various processes for preventing the falling off (i.e. for the fixation) of the absorbent polymer have heretofore been proposed.
The prior-art processes heretofore proposed for preventing the falling off i.e. for the fixation of the absorbent polymer comprises bonding the absorbent polymer to a base to be combined therewith by a means such as:
(1) the bonding of the absorbent polymer to the base with water, PA1 (2) the application of an adhesive to the base followed by the adhesion of the absorbent polymer thereto to form a sandwich structure, or PA1 (3) the bonding of the absorbent polymer by means of a heat-fusible fiber (non-woven fabric) or film.
The first bonding means (1) was proposed, for examples, in Japanese Patent Publication No. 2647/1984 and Japanese Patent Laid-Open Nos. 123293/1979 and 141099/1979. However, these processes wherein the absorbent polymer is swollen with water and fixed have problems in that when the absorbent polymer is impregnated with water in a quantity sufficient for fixation to soften the gel before fixation, the absorbent polymer is crushed in the fixing step to impair the essential absorbent properties of the absorbent polymer and, in addition, the water cannot be evenly spread in the entire absorbent polymer layer and the part of the absorbent polymer layer in which the gel adhesion is insufficient, falls off.
The second bonding means (2) was proposed, for example, in Japanese Patent Laid-Open No. 63043/1985. In this process wherein the absorbent polymer is bonded to the base by means of an adhesive, the absorbent polymer can be prevented from falling off to a considerable extent. However, it also has the defects that since the hydrophilic properties of the adhesive are insufficient, the absorbency of the base is seriously reduced and, as a result, the properties of the absorbent polymer cannot be sufficiently exhibited and that since the absorbent polymer is completely fixed to the base, it cannot be released from fixation and, therefore, the swelling of the absorbent polymer is inhibited, thereby seriously lowering the absorption rate.
The third bonding means (3) was proposed, for example, in Japanese Patent Laid-Open Nos. 158096/1979 and 14024/1980. However, these processes also have the problem of impairing the properties of the absorbent polymer as described in the above item (2).
Thus it has been demanded in the prior art to develop a process which satisfies the two requirements, i.e. the prevention of the falling off of the absorbent polymer without sacrificing the absorbing properties of the absorbent polymer per se.